1. Field of the Invention
The present invention relates to a 3GPP universal mobile telecommunications system (UMTS) and, more particularly, to a method for updating a radio link parameter in a system providing a high speed downlink packet access (HSDPA) service.
2. Description of the Background Art
In order to support a high speed packet data service in downlink, in third generation partnership project (3GPP) UMTS system, there is a transport channel called a high speed downlink shared channel (HS-DSCH). The HS-DSCH is used in a system supporting a high speed downlink packet access (HSDPA). The HS-DSCH uses a short transmission time interval (TTI) (3 slot, 2 ms) and supports various modulation code sets (MCS) to support a high data rate. That is, the UMTS system can attain optimum data transmission performance by selecting MCS based on channel condition and using Hybrid ARQ that combines automatic repeat request (ARQ) and coding techniques.
The HS-DSCH transmits a high speed user data at every sub-frame of 2 ms. The transport channel, HS-DSCH, is mapped onto a physical channel called a high speed physical downlink shared channel (HS-PDSCH).
For transmission of user data through the HS-DSCH, control information should be transmitted. The control information is transmitted through the downlink (DL) shared control channel (HS-SCCH) and the uplink (UL) dedicated physical control channel (HS-DPCCH).
The downlink shared control channel (HS-SCCH) is a type of a downlink (DL) common control channel to support the HSDPA technique. The DL HS-SCCH is a downlink physical channel with spreading factor of 128 and data rate of 60 kbps. The HS-SCCH is used to transmit a UE ID (identification) and control information so that the UE can receive HS-DSCH transmitting a high speed user data after receiving HS-SCCH.
FIG. 1 illustrates a frame structure of the uplink HS-DPCCH.
With reference to FIG. 1, the uplink HS-DPCCH is constructed with a radio frame with a period (Tf) of 10 ms and each radio frame consists of five subframes of 2 ms. One sub-frame consists of three slots.
The uplink HS-DPCCH transmits an uplink feedback signaling related to transmission of a downlink HS-DSCH data. The uplink feedback signaling generally includes ACK (acknowledgement)/NACK (negative acknowledgement) information for the HARQ and a channel quality indicator (CQI). The ACK/NACK information is transmitted at the first slot of the HS-DPCCH sub-frame and the CQI is transmitted at the second and third slots of the HS-DPCCH sub-frame. The HS-DPCCH is always configured with the UL DPCCH. The ACK/NACK informs ACK or NACK information for a user data packet transmitted through the DL HS-DSCH according to the HARQ mechanism, and the CQI transmits status information of the downlink radio channel obtained from the measurement of the DL CPICH (Common Pilot Channel) in the UE, to a base station.
FIG. 2 illustrates a structure of a UMTS radio access network (UTRAN).
With reference to FIG. 1, the UTRAN includes a serving RNC (SRNC) and a drift RNC (DRNC) that control a base station (a node B). In a soft handover, the terminal (UE) maintains radio links with base stations connected to the SRNC and the DRNC. In this case, the base station (node B) and RNC (the SRNC and the DRNC) are connected over the lub interface, and the SRNC and the DRNC are connected over the lur interface. An interface between the SRNC and a core network (CN) is referred to the lu interface.
In general, the radio network controller (RNC) directly manages the node B and is classified into a controlling RNC (CRNC) (not shown) managing a common radio resource and a serving RNC (SRNC) managing a dedicated radio resource assigned to respective UEs 122.
The DRNC exists in a drift radio network subsystem (DRNS) and, if the UE moves from a region covered by the SRNC to a region covered by the DRNC, the DRNC provides its own radio resource to the UE.
In the UTRAN, a radio access interface protocol is divided into a control plane and a user plane. The user plane is a domain where user traffic such as voice or an IP packet is transmitted. The control plane is a domain where control information is transmitted.
FIG. 3 illustrates a control plane protocol in the UTRAN.
With reference to FIG. 2, the control plane protocol includes a radio resource control (RRC) protocol used between the UE and the RNC, a node B application part (NBAP) protocol used between the base station (node B) and the RNC, and a radio network subsystem application part (RNSAP) protocol used between the RNC and the core network (CN). The NBAP, RNSAP and RANAP protocols can contain various control messages between the base station and RAN, between the RNCs and between the core network and the RNC. In case that the control message is transmitted in the user plane, it is transmitted as a type of control frame of frame protocol, while in case that the control message is transmitted in the control plane, it is transmitted as a type of NBAP or RNSAP message.
FIG. 4 shows an example procedure for configuration of the HS-DSCH channel when the dedicated channel (DCH) is configured in the UE.
First of all, a radio link (RL) for the HS-DSCH is reconfigured. For this purpose, the SRNC sends an RL reconfiguration prepare message to the DRNC to initiate the RL reconfiguration procedure (step S102).
The DRNC sends the RL reconfiguration prepare message to each node B to request each node B to prepare a synchronized RL reconfiguration procedure (step S104). Then, the corresponding node B configures a radio resource for the HS-DSCH and sends an RL reconfiguration ready message as a response to the RL reconfiguration prepare message (step S106).
After the DRNC completes the preparation of RL reconfiguration, it sends an RL reconfiguration ready message to the SRNC (step S108). The SRNC sends an RL reconfiguration commit message to the DRNC (step S110), and the DRNC sends the RL reconfiguration commit message to the node B (step S112).
Through these steps, a radio link and a transport bearer for HS-DSCH are configured. That is, an ALCAP lub transport bearer is set between the node B and the DRNC, and an ALCAP lur transport bearer is set between the DRNC and the SRNC.
After the setup of the radio link is completed, the SRNC sends a radio bearer reconfiguration message to the UE to set up an HS-DSCH (step S114), and the UE responds thereto with a radio bearer reconfiguration complete message (step S116). Such messages are sent as an RRC (radio resource control) message.
With those steps completed, an HS-DSCH transport channel is set up and an MAC-hs sub-layer is constructed in the node B to manage HS-DSCH transmission.
Thereafter, when there is a downlink data to be transmitted, the SRNC sends an HS-DSCH capacity request control frame to the DRNC (step S118) and the DRNC forwards the corresponding message to the node B (step S120). Then, the node B determines the amount of data that can be sent for the HS-DSCH and reports the determined information to the DRNC through a HS-DSCH capacity allocation control frame of a frame protocol (step S122), and the DRNC sends the HS-DSCH capacity allocation control frame to the SRNC (step S124).
Afterwards, the SRNC starts to send downlink data to the node B (step S126) and the node B initiates transmission of the downlink data through the HS-DSCH. That is, the node B transmits signaling information related to the HS-PDSCH to the UE through the shared control channel (HS-SCCH) (step S128) and transmits the HS-DSCH data to the UE through the HS-PDSCH (step S130).
With reference to FIG. 6, if the DCH is not configured, the radio link setup procedure is used in place of the radio link (RL) reconfiguration procedure.
A detailed physical layer procedure that the UE transmits a feedback signal (ACK or NACK) through the HS-DPCCH after receiving the HS-DSCH data is as follows:
The UE monitors a UE ID transmitted through HS-SCCH to recognize whether there is data it is to receive. Then, if there is data it is to receive, the UE receives the control information transmitted through the HS-SCCH and the HS-DSCH data transmitted through the HS-PDSCH using the received control information. The UE decodes the received HS-PDSCH data, checks a CRC, and transmits ACK or NACK to a base station according to the CRC check result.
At this time, the UE can repeatedly transmits ACK/NACK during multiple consecutive HS-DPCCH sub-frames. The number of the consecutive HS-DPCCH sub-frames for ACK/NACK repetition is equal to a repetition factor of ACK/NACK, N_acknack_transmit. If, however, the UE fails to acquire control information corresponding to itself from the monitored HS-SCCH, it does not transmit ACK/NACK to the base station.
In addition, the UE measures a common pilot channel (CPICH) and transmits a channel quality indicator (CQI) value the UE repeatedly transmits CQI during multiple consecutive HS-DPCCH sub-frames. The number of the consecutive HS-DPCCH sub-frames for CQI repetition is equal to a repetition factor of CQI, N_cqi_transmit.
As afore-mentioned, in the conventional HSDPA system, the radio link parameter updating process is initiated only by the RNC. That is, the RNC detects/determines whether update of a parameter for a radio link is necessary, and if the parameter needs to be updated, the RNC sends an updated radio parameter value to the node B. In other words, the node B can not update the HS-DPCCH parameters by its own decision but can merely update the HS-DPCCH parameters only through the radio bearer reconfiguration procedure the RNC triggers.
However, in the HSDPA system, a HSDPA scheduler exists in the node B, so that it should be possible that a HSDPA scheduler updates the HS-DPCCH parameters by its own decision even without an initiation of the RNC if the update is necessary.
In the case that the RNC starts updating the HS-DPCCH related parameter (i.e., ACK/NACK, and the period and repetition information of CQI, etc.), the HSDPA scheduler of the node B can not control on its own the ACK/NACK transmission and the CQI reporting according to channel condition for the UE (terminal). Thus, the conventional parameter updating method is disadvantageous in that the HSDPA scheduling is limited and the radio resource is inefficiently used.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.